Heretofore, a bean-juice-manufacturing caldron used to the manufacture of soybean milk, a soybean curd and membrane like soybean curds comprises a cylindrical caldron main body having closed upper and lower ends, a charge port disposed at lower portion of the caldron main body for charging a raw material of bean juice such as ground soybeans to which water is added or the heated ones thereof, a discharge port disposed at upper portion of the caldron main body for discharging the raw material after it is processed in the caldron, and a steam injection pipe having a plurality of injection ports simply formed therethrough and installed in interior of the caldron main body.
Steam used in the conventional bean-juice-manufacturing caldron has been air-containing steam obtained by simply heating ordinary water.
In the conventional bean-juice-manufacturing caldron, the steam injected from the injection ports of the steam injection pipe are injected in a radial direction. The steam injected in the radial direction collides against the inner peripheral wall of the caldron main body and lose their motion energy so that the flow rate of the streams is reduced. Therefore, the steam having the reduced flow rate cannot sufficiently turn and flow into the space located backward of the injection ports in the caldron main body and the steam only move upward in the caldron main body. As a result, the steam is in good contact with the raw material of bean juice or the heated one thereof (hereinafter, they are referred to as raw material of bean juice as a whole) which is located in the vicinity of the radially injecting passages of the steam which are directed radially from the injection ports so that the raw material of bean juice located at the position is sufficiently heated with the heat of the steam. However, since the steam comes into contact with the raw material of bean juice in a small quantity which is located in the space backward of the injection ports of the caldron main body, the heat of the steam is not sufficiently transmitted to the raw material of bean juice located at the backward position. Thus, the raw material of bean juice cannot be heated with a necessary quantity of heat. As a result, there is caused thereby a problem that a part of the raw material of bean juice is sufficiently heated and the other part thereof is insufficiently heated, whereby the raw material of bean juice is unevenly boiled.
In the conventional bean-juice-manufacturing caldron, since steam cannot be uniformly and sufficiently supplied to the raw material of bean juice, the steam cannot sufficiently transmit their heat to the raw material of bean juice. Accordingly, a large quantity of the steam stays in the upper portion of the caldron main body while holding a sufficient quantity of heat at high temperature and increase the pressure of the upper portion of the caldron main body as residual steam. Thus, there arises a problem that the raw material of bean juice is pushed out into the discharge port of the caldron main body in a quantity larger than necessary, the feed of the raw material of bean juice in the caldron main body cannot be properly controlled, the raw material of bean juice has a portion to which the heat of the stream is transmitted well and which is sufficiently heated and a portion which is insufficiently heated, whereby the raw material of bean juice is unevenly boiled, bean juice of good quality cannot be produced and thus a soybean curd of good quality cannot be manufactured.
Incidentally, soybean milk obtained by separately a solid soybean curd lees ("okara") from a sufficiently heated bean juice (of high quality) not only promptly reacts to a coagulant or a curding agent but also is mixed therewith quickly as compared with the soybean milk obtained by separately the solid soybean curd lees from an insufficiently heated bean juice (of low quality). Therefore, when a curding agent such as magnesium chloride which is usually used as aqueous solution ("nigari") or the like is added to soybean milk manufactured from an unevenly boiled bean juice in the manufacture of a soybean curd, the curding agent is concentrated at the portion of the soybean milk which was obtained from the sufficiently heated portion of the bean juice before a coagulating reaction occurs to the entire soybean milk, the soybean milk is reacted to the curding agent promptly, and thus the curding agent cannot be uniformly mixed with the entire soybean milk. As a result, there is a problem that a soybean curd of high quality having elasticity and a sufficient water keeping property cannot be still more manufactured.
Further, the problem of the uneven boiling of beans is not limited to the case in which bean juice is manufactured and it arises when ordinary foodstuffs such as grains and the like are added with water and boiled. In particular, a problem arises when beans are boiled unevenly. F or example, unevenly boiled adzuki beans cause a problem in the manufacture of powder bean jam of high quality.
Incident ally, since steam is obtained by simply heating ordinary water in the conventional bean-juice-manufacturing caldron, it cannot be avoided for air to be mixed with the steam when it is manufactured so that oxygen is contained in the steam. When a raw material of the bean juice is boiled with the steam in which the oxygen is mixed, it is also mixed with or dissolved in soybean milk obtained by separating an solid soybean curd lees from bean juice. Thus, there is a problem that bacteria and so forth are propagated in the soybean milk, the soybean milk is deteriorated in a very short period of time and a soybean curd of high quality cannot be manufactured from the soybean milk as well as a lot of porosities are formed in the soybean curd due co the dissolved oxygen and the taste thereof becomes deterigated. To cope with this problem, a fresh soybean milk must be used at once for the manufacture of a soybean curd. Thus, a soybean curd of high quality is manufactured only by a speciality manufacturers and it is impossible to supply a fresh soybean curd to homes and eating houses.
Further, soybean milk is an excellent drink which does not cause atopic dermatitis and allergy symptoms different from a cow's milk regardless of that it is as nutritious as the cow's milk and less expensive. However, a fresh soybean milk manufactured from the conventional bean-juice-manufacturing caldron cannot be stored for a long time unless it is sterilized at high temperature. However, when the soybean milk is sterilized at high temperature, it is somewhat denatured and the deliciousness characteristic to the soybean milk is lost. Consequently, there is also a problem that a fresh soybean milk having deliciousness and a good taste is sold only in the vicinity of a small-scaled speciality soybean curd manufacturers in a very small quantity and cannot be freely distributed in a market.
A main subject of the present invention is to solve the problems of the conventional technique and to provide a caldron capable of manufacturing a boiled raw material of high quality such as bean juice, boiled adzuki beans and the like by preventing a water-added raw material to be boiled such as a raw material of bean juice, adzuki beans immersed in water or a heated ones of the adzuki beans from being unevenly boiled, by eliminating an adverse affect caused by the steam remaining in the caldron, by lowering the pressure in a caldron main body in a range higher than atmospheric pressure and preferably reducing the pressure in a range lower than it, by properly controlling the raw material fed in the caldron main body, and by evenly and sufficiently heating the raw material with the heat of the steam which are uniformly and sufficiently transmitted thereto.
Another subject of the present invention is to provide, in addition to the above subject, a caldron capable of manufacturing a boiled raw material such as bean juice and the like in and with which no oxygen is dissolved and mixed by supplying superheated steam containing substantially no oxygen when the boiled raw material such as the bean juice and the like is manufactured, and, as a result, capable of obtaining a liquid separated from the boiled raw material such as soybean milk and the like in and with which no oxygen is dissolved and mixed and which can be stored for a long period of time.